Experimental study of CO2-Assisted Gravity Drive in Conglomerate reservoir with Full-diameter cores

Abstract To investigate the influence of CO 2 -assisted gravity drive injection parameters on oil recovery in conglomerate reservoirs, full-diameter conglomerate cores were utilized to conduct experiments under varying inclinations, pressures, and injection velocities. Nuclear magnetic resonance (NMR) scanning technology was employed to analyze changes in oil distribution characteristics before and after gas flooding. The experimental results indicate that inclination has the most significant impact on oil recovery, followed by injection velocity; conversely, increasing pressure exerts a relatively minor effect on oil displacement efficiency until miscibility is achieved. Generally, oil recovery increases with greater inclination angles, resulting in a notable delay in gas breakthrough time. In vertical dip scenarios, oil recovery improved from 43.4% to 58.2% compared to horizontal dip conditions, reflecting a 23.3% increase in sweep efficiency. When pressure was elevated from 13 MPa to 20 MPa, the increase in oil recovery was limited to just 6.8 percentage points. Furthermore, upon increasing the injection velocity fivefold, there was a decrease in oil recovery from 47.6% to 39.8%, representing a reduction of 7.8%, while simultaneously accelerating the gas breakthrough time. NMR scanning results reveal that CO 2 predominantly targets reservoir regions with pore radii exceeding 0.1 μ m. Due to the gravitational segregation effects inherent in gravity drive processes, sweep efficiency at both the top and bottom sections can exceed 90%.